Anyone else experienced these allen bolts being as soft as toffee? Tried tapping a slightly larger allen key in and screwing a bolt extractor in too. But to no avail. Any thoughts?

Epoxy? Torx key?

What about wacking a bigger torx head – usually work for me? And yes the stainless ones are soft 🙂

impact driver? heat?

Mole grips on out side of head or try a serch for boa extractors.I've used them for getting a disc bolt out, you should be able to put one in the damaged head and drill them out slowly that's if the mole grips cant turn it out or the head is domed.

Hammer a sacrificial torx bit in. Will bite into the head much more effectively than a hex bit. Don't try turning it yet. Patience…..

Soak overnight with quality penetrating fluid

Freeze release spray in the morning (Disclaimer: may damage paintwork!!!)

Only then try turning the torx bit

Do this before trying any sort of stud extractor. If you snap a hardened steel stud extractor off in it, you are gonna have a hell of a task trying to get that out.

I've never snapped a stud extractor yet? 😯

I've snapped a few

Reverse-threaded type extractors are good for above M6 but risky in badly seized bolts of small diameters. The splined extractors are less risky because you at least have a chance to punch em through (or pull out if splines break) Although that does depend on what the situation is.

Other problem with reverse threaded extractors is, the more force you apply to em, the more they expand into whatever your screwing em into – which can defeat the object. Obviously situation dependant…and depends on how badly seized whatever it is you're trying to extract.

Not saying they shouldn't be used, just to be aware that if they snap, you are royally ****. So worth exploring some other options first.

I use these for my cap head problems as I tend to just keep the extractor in the damaged hex part.
http://cpc.farnell.com/1/1/27285-bolt-remover-4-piece-kit-drill-out-17040-boa.html

these are what i've used for removing small allen/torx head bolts when all else has failed.

Did the same on mine. Carefully saw a slot in the head of the bolt (you can do this when the caliper is still on the bike) and then use a screwdriver to undo them. No need to replace the bolt then either, cos they are an odd length and only partly threaded.